Glycoconjugate vaccines

ABSTRACT

The disclosure relates to a glycoconjugate vaccine conferring protection against  Francisella tularensis  infections and a method to manufacture a glycoconjugate antigen.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 14/655,210 filed Jun. 24, 2015, which is the U.S. National Stage of International Application No. PCT/GB2014/050159, filed Jan. 21, 2014, which was published in English under PCT Article 21(2), which in turn claims the benefit of United Kingdom Application No. 1301085.5, filed Jan. 22, 2013.

FIELD OF THE INVENTION

The disclosure relates to a glycoconjugate vaccine conferring protection against Francisella tularensis infections and a method to manufacture a glycoconjugate antigen.

BACKGROUND TO THE INVENTION

Vaccines protect against a wide variety of infectious diseases. Many vaccines are produced by inactivated or attenuated pathogens which are injected into a subject, whereas others, so called ‘subunit vaccines’, are made from proteins or polysaccharides displayed on the surface of the pathogen. Subunit vaccines are preferred over inactivated or attenuated pathogens as they tend to cause fewer side effects. However, the development and production of a subunit vaccine requires the identification and isolation of protective antigens from the pathogenic organism, and moreover subunit vaccines based on polysaccharide antigens invoke often a T-cell independent immune response which results in low antibody titre, short half-life of the antibodies and low affinity for a specific antigen.

The development of subunit vaccines is an active research area and it has been recognized that the immunogenicity of polysaccharide antigens can be enhanced by conjugation to a protein carrier. Glycoconjugates have the ability to induce both humoral and adaptive immune responses. Currently licensed human glycoconjugate vaccines include those against Haemophilus influenzae, Neisserria meningitidis and Streptococcus pneumoniae, by which bacterial polysaccharides are chemically bound to carrier proteins. The H. influenzae type B (Hib) vaccine or Prevnar®, a β-valent capsule-based glycoconjugate vaccine protective against diseases caused by S. pneumonia, employs the carrier protein iCRM197, a non-toxic version of diphtheria toxin isolated from Corynebacterium diphtheria.

Although these vaccines are effective, their production requires both the purification of polysaccharide glycan from the native pathogen and the chemical coupling of the sugar to a suitable protein carrier, which can lead to impure products, low yields, variation between batches of conjugates and poses a biohazard as the handling of the pathogenic organism is unavoidable. This process is highly costly, inefficient and time consuming. The use of organic systems represents a more rapid and economical method for the production of glycoconjugates.

So far several pathogenic bacteria have been identified forming glycoproteins and the genes involved identified. The gram negative pathogenic bacterium Campylobacter jejuni harbours a gene cluster involved in the synthesis of lipo-oligosaccharides and N-linked glycoproteins. The protein glycosylation locus, a cluster of 12 genes comprising pgIA-pgIG, is involved in the glycosylation of over 30 glycoproteins. Part of the gene cluster is PgIB, an oligosaccharyltransferase catalysing the transfer of glycans on to a wide range of different non-species related protein acceptors, indicating broad substrate specificity. Moreover PgIB when expressed in E. coli has been used to produce novel glycoconjugates providing a genetic tool to express heterologous recombinant glycoproteins. Production of glycoconjugate vaccines in a bacterial system are disclosed in patent application WO2009/104074. Glycoconjugates comprising a protein carrier and an antigenic polysaccharide O-antigen form Shigella, E. coli and Pseudomonas aeruginosa using the oligosaccharyltransferase PgIB were produced, and bioconjugates against the Shigella O1 polysaccharide were shown to elicit an immune response.

Tularemia, also known as lemming or rabbit fever, is common in wild rodents and can be passed on to humans by contact with infected animal tissues, ticks or biting flies, or by inhalation of the infectious organism. Tularemia is found in North America, parts of Europe and Asia and is caused by the gram-negative coccobacillus Francisella tularensis. F. tularensis is highly infectious, with a mortality rate of up to 30% and based on the above listed characteristics classified as a Class A bioterrorism agent. Tularemia is difficult to diagnose, however, can be treated although with varying success with antibiotics. There are no vaccines available yet.

Recent studies suggest a protective effect using purified lipopolysaccharide (LPS) comprising an O-antigen from F. tularensis in a murine infection model; however, the development of glycoprotein vaccines protecting against highly infectious pathogens to high quantities using current methods are associated with high safety concerns.

We disclose a novel bacterial protein glycan coupling technology (PGCT) that allows the production of protective vaccines from the highly virulent wild-type strain of F. tularensis holarctica. The recombinant glycoconjugate was easily purified and was capable of providing significant protection against subsequent challenge when compared to LPS based vaccine treatments.

STATEMENT OF INVENTION

According to an aspect of the invention there is provided a vaccine composition comprising: a carrier polypeptide comprising one or more T-cell dependent epitopes and one or more amino acid sequences having the amino acid motif D/E-X-N-X-S/T wherein X is any amino acid except proline and crosslinked to said carrier polypeptide an antigenic polysaccharide wherein the polysaccharide is isolated from Francisella and is an O-antigen.

According to an aspect of the invention there is provided an immunogenic composition comprising: a carrier polypeptide comprising one or more T-cell dependent epitopes and one or more amino acid sequences having the amino acid motif D/E-X-N-X-S/T wherein X is any amino acid except proline and crosslinked to said carrier polypeptide is an antigenic polysaccharide wherein the polysaccharide is isolated from Francisella and is an O-antigen.

In a preferred embodiment of invention said O-antigen comprises 4)-α-D-GalNAcAN-(1-4)-α-D-GalNAcAN-(1-3)-β-D-QuiNAc-(1-2)-β-D-Qui4NFm-(1-), where GalNAcAN is 2-acetamido-2-deoxy-O-D-galact-uronamide, 4NFm is 4,6-dideoxy-4-formamido-D-glucose and the reducing end group QuiNAc is 2-acetamido-2,6-dideoxy-O-D-glucose.

In a preferred embodiment of the invention said O-antigen is a tetrasaccharide.

In a preferred embodiment of the invention said protein carrier comprises an amino acid sequence as set forth in of SEQ ID NO: 1.

In a preferred embodiment of the invention said protein carrier comprises an amino acid sequence as set forth in of SEQ ID NO: 2.

In a preferred embodiment of the invention said protein carrier comprises an amino acid sequence as set forth in of SEQ ID NO: 3.

In a preferred embodiment of the invention said protein carrier comprises an amino acid sequence as set forth in of SEQ ID NO: 4.

In a preferred embodiment of the invention said protein carrier comprises an amino acid sequence as set forth in of SEQ ID NO: 5.

In a preferred embodiment of the invention said protein carrier comprises an amino acid sequence as set forth in of SEQ ID NO: 6.

In a preferred embodiment of the invention said composition includes an adjuvant.

In a preferred embodiment of the invention said adjuvant is selected from the group consisting of: cytokines selected from the group consisting of e.g. GMCSF, interferon gamma, interferon alpha, interferon beta, interleukin 12, interleukin 23, interleukin 17, interleukin 2, interleukin 1, TGF, TNFα, and TNFβ.

In a further alternative embodiment of the invention said adjuvant is a TLR agonist such as CpG oligonucleotides, flagellin, monophosphoryl lipid A, poly I:C and derivatives thereof.

In a preferred embodiment of the invention said adjuvant is a bacterial cell wall derivative such as muramyl dipeptide (MDP) and/or trehalose dycorynemycolate (TDM).

An adjuvant is a substance or procedure which augments specific immune responses to antigens by modulating the activity of immune cells. Examples of adjuvants include, by example only, agonistic antibodies to co-stimulatory molecules, Freunds adjuvant, muramyl dipeptides, liposomes. An adjuvant is therefore an immunomodulator. A carrier is an immunogenic molecule which, when bound to a second molecule augments immune responses to the latter. The term carrier is construed in the following manner. A carrier is an immunogenic molecule which, when bound to a second molecule augments immune responses to the latter. Some antigens are not intrinsically immunogenic yet may be capable of generating antibody responses when associated with a foreign protein molecule such as keyhole-limpet haemocyanin or tetanus toxoid. Such antigens contain B-cell epitopes but no T cell epitopes. The protein moiety of such a conjugate (the “carrier” protein) provides T-cell epitopes which stimulate helper T-cells that in turn stimulate antigen-specific B-cells to differentiate into plasma cells and produce antibody against the antigen. Helper T-cells can also stimulate other immune cells such as cytotoxic T-cells, and a carrier can fulfil an analogous role in generating cell-mediated immunity as well as antibodies.

In a preferred embodiment of the invention said composition includes at least one additional anti-bacterial agent.

In a preferred embodiment of the invention said additional anti-bacterial agent is a different antigenic molecule.

In a preferred embodiment of the invention said composition is a multivalent antigenic composition.

In an alternative preferred embodiment of the invention said additional anti-bacterial agent is an antibiotic.

According to a further aspect of the invention there is provided a vaccine composition according to the invention for use in the prevention or treatment of a Francisella infection.

Preferably said infection is caused by Francisella tularensis.

According to a further aspect of the invention there is provided a method to treat a Francisella infection comprising administering an effective amount of a vaccine or immunogenic composition according to the invention.

Preferably said infection is caused by Francisella tularensis.

According to an aspect of the invention there is provided an antigenic polypeptide comprising: a carrier polypeptide comprising one or more T-cell dependent epitopes and one or more amino acid sequences having the amino acid motif D/E-X-N-X-S/T wherein X is any amino acid except proline and crosslinked to said carrier polypeptide is an antigenic polysaccharide wherein the polysaccharide is isolated from Francisella and is an O-antigen.

In a preferred embodiment of the invention said O-antigen comprises 4)-α-D-GalNAcAN-(1-4)-α-D-GalNAcAN-(1-3)-β-D-QuiNAc-(1-2)-β-D-Qui4NFm-(1-), where GalNAcAN is 2-acetamido-2-deoxy-O-D-galact-uronamide, 4NFm is 4,6-dideoxy-4-formamido-D-glucose and the reducing end group QuiNAc is 2-acetamido-2,6-dideoxy-O-D-glucose.

According to a further aspect of the invention there is provided a modified bacterial cell wherein said cell is genetically modified to include:

-   -   i) a nucleic acid molecule comprising the nucleotide sequence of         the Francisella O-antigen biosynthetic polysaccharide locus [SEQ         ID NO: 7];     -   ii) a nucleic acid molecule comprising a nucleotide sequence of         an oligosaccharyltransferase [SEQ ID NO: 8] or a functional         variant thereof wherein said variant comprises a nucleic acid         molecule the complementary strand of which hybridizes under         stringent hybridization conditions to the sequence set forth in         SEQ ID NO: 8 and wherein said nucleic acid molecule encodes an         oligosaccharyltransferase; and/or     -   iii) a nucleic acid molecule comprising a nucleotide sequence of         an oligosaccharyltransferase [SEQ ID NO: 16] or a functional         variant thereof wherein said variant comprises a nucleic acid         molecule the complementary strand of which hybridizes under         stringent hybridization conditions to the sequence set forth in         SEQ ID NO: 16 and wherein said nucleic acid molecule encodes an         oligosaccharyltransferase; and     -   iv) a nucleic acid molecule comprising a nucleotide sequence of         carrier polypeptide wherein the a carrier polypeptide comprising         one or more T-cell dependent epitopes and one or more amino acid         sequences having the amino acid motif D/E-X-N-X-S/T wherein X is         any amino acid except proline, wherein said bacterial cell is         adapted for expression of each nucleic acid molecule and         synthesizes an antigenic polypeptide according to the invention.

Hybridization of a nucleic acid molecule occurs when two complementary nucleic acid molecules undergo an amount of hydrogen bonding to each other. The stringency of hybridization can vary according to the environmental conditions surrounding the nucleic acids, the nature of the hybridization method, and the composition and length of the nucleic acid molecules used. Calculations regarding hybridization conditions required for attaining particular degrees of stringency are discussed in Sambrook et al., Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 2001); and Tijssen, Laboratory Techniques in Biochemistry and Molecular Biology—Hybridization with Nucleic Acid Probes Part I, Chapter 2 (Elsevier, N.Y., 1993). The Tm is the temperature at which 50% of a given strand of a nucleic acid molecule is hybridized to its complementary strand.

The following is an exemplary set of hybridization conditions and is not limiting.

Very High Stringency (Allows Sequences that Share at Least 90% Identity to Hybridize)

-   -   i) Hybridization: 5×SSC at 65° C. for 16 hours     -   ii) Wash twice: 2×SSC at room temperature (RT) for 15 minutes         each     -   iii) Wash twice: 0.5×SSC at 65° C. for 20 minutes each

High Stringency (Allows Sequences that Share at Least 80% Identity to Hybridize)

-   -   i) Hybridization: 5×-6×SSC at 65° C.-70° C. for 16-20 hours     -   ii) Wash twice: 2×SSC at RT for 5-20 minutes each     -   iii) Wash twice: 1×SSC at 55° C.-70° C. for 30 minutes each

Low Stringency (Allows Sequences that Share at Least 50% Identity to Hybridize)

-   -   i) Hybridization: 6×SSC at RT to 55° C. for 16-20 hours     -   ii) Wash at least twice: 2×-3×SSC at RT to 55° C. for 20-30         minutes each.

A variant oligosaccharyltransferase polypeptide as herein disclosed may differ in amino acid sequence by one or more substitutions, additions, deletions, truncations that may be present in any combination. Among preferred variants are those that vary from a reference polypeptide [SEQ ID NO: 9, SEQ ID NO: 17] by conservative amino acid substitutions. Such substitutions are those that substitute a given amino acid by another amino acid of like characteristics. The following non-limiting list of amino acids are considered conservative replacements (similar): a) alanine, serine, and threonine; b) glutamic acid and aspartic acid; c) asparagine and glutamine d) arginine and lysine; e) isoleucine, leucine, methionine and valine and f) phenylalanine, tyrosine and tryptophan. Most highly preferred are variants that retain or enhance the same biological function and activity as the reference polypeptide from which it varies.

In one embodiment, the variant polypeptides have at least 40% or 45% identity, more preferably at least 50% identity, still more preferably at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% identity, or at least 99% identity with the full length amino acid sequence illustrated herein.

In a preferred embodiment of the invention at least the oligosaccharyltransferase of ii) or iii) above is integrated into the bacterial genome to provide a stably transfected and expressing oligosaccharyltransferase.

In a further preferred embodiment of the invention one or more nucleic acid molecules encoding carrier polypeptides are also integrated into the bacterial genome.

According to a further aspect of the invention there is provided a bacterial cell culture comprising a genetically modified bacterial cell according to the invention.

According to a further aspect of the invention there is provided a process for the production of one or more glycoconjugates comprising:

-   -   i) providing a bacterial cell culture according to the         invention;     -   ii) providing cell culture conditions; and     -   iii) isolating one or more glyconjugates from the bacterial cell         or cell culture medium.

According to a further aspect of the invention there is provided a cell culture vessel comprising a bacterial cell culture according to the invention.

In a preferred embodiment of the invention said cell culture vessel is a fermentor.

Bacterial cultures used in the process according to the invention are grown or cultured in the manner with which the skilled worker is familiar, depending on the host organism. As a rule, bacteria are grown in a liquid medium comprising a carbon source, usually in the form of sugars, a nitrogen source, usually in the form of organic nitrogen sources such as yeast extract or salts such as ammonium sulfate, trace elements such as salts of iron, manganese and magnesium and, if appropriate, vitamins, at temperatures of between 0° C. and 100° C., preferably between 10° C. and 60° C., while gassing in oxygen.

The pH of the liquid medium can either be kept constant, that is to say regulated during the culturing period, or not. The cultures can be grown batchwise, semi-batchwise or continuously. Nutrients can be provided at the beginning of the fermentation or fed in semi-continuously or continuously. The products produced can be isolated from the bacteria as described above by processes known to the skilled worker, for example by extraction, distillation, crystallization, if appropriate precipitation with salt, and/or chromatography. In this process, the pH value is advantageously kept between pH 4 and 12, preferably between pH 6 and 9, especially preferably between pH 7 and 8.

An overview of known cultivation methods can be found in the textbook Bioprocess technology 1. Introduction to Bioprocess technology (Gustav Fischer Verlag, Stuttgart, 1991) or in the textbook by Storhas (Bioreaktoren and periphere Einrichtungen [Bioreactors and peripheral equipment] (Vieweg Verlag, Brunswick/Wiesbaden, 1994)).

The culture medium to be used must suitably meet the requirements of the bacterial strains in question. Descriptions of culture media for various bacteria can be found in the textbook “Manual of Methods for General Bacteriology” of the American Society for Bacteriology (Washington D.C., USA, 1981).

As described above, these media which can be employed in accordance with the invention usually comprise one or more carbon sources, nitrogen sources, inorganic salts, vitamins and/or trace elements.

Preferred carbon sources are sugars, such as mono-, di- or polysaccharides. Examples of carbon sources are glucose, fructose, mannose, galactose, ribose, sorbose, ribulose, lactose, maltose, sucrose, raffinose, starch or cellulose. Sugars can also be added to the media via complex compounds such as molasses or other by-products from sugar refining. The addition of mixtures of a variety of carbon sources may also be advantageous. Other possible carbon sources are oils and fats such as, for example, soya oil, sunflower oil, peanut oil and/or coconut fat, fatty acids such as, for example, palmitic acid, stearic acid and/or linoleic acid, alcohols and/or polyalcohols such as, for example, glycerol, methanol and/or ethanol, and/or organic acids such as, for example, acetic acid and/or lactic acid.

Nitrogen sources are usually organic or inorganic nitrogen compounds or materials comprising these compounds. Examples of nitrogen sources comprise ammonia in liquid or gaseous form or ammonium salts such as ammonium sulfate, ammonium chloride, ammonium phosphate, ammonium carbonate or ammonium nitrate, nitrates, urea, amino acids or complex nitrogen sources such as cornsteep liquor, soya meal, soya protein, yeast extract, meat extract and others. The nitrogen sources can be used individually or as a mixture.

Inorganic salt compounds which may be present in the media comprise the chloride, phosphorus and sulfate salts of calcium, magnesium, sodium, cobalt, molybdenum, potassium, manganese, zinc, copper and iron.

Inorganic sulfur-containing compounds such as, for example, sulfates, sulfites, dithionites, tetrathionates, thiosulfates, sulfides, or else organic sulfur compounds such as mercaptans and thiols may be used as sources of sulfur for the production of sulfur-containing fine chemicals, in particular of methionine.

Phosphoric acid, potassium dihydrogen phosphate or dipotassium hydrogen phosphate or the corresponding sodium-containing salts may be used as sources of phosphorus.

Chelating agents may be added to the medium in order to keep the metal ions in solution. Particularly suitable chelating agents comprise dihydroxyphenols such as catechol or protocatechuate and organic acids such as citric acid.

The fermentation media used according to the invention for culturing bacteria usually also comprise other growth factors such as vitamins or growth promoters, which include, for example, biotin, riboflavin, thiamine, folic acid, nicotinic acid, panthothenate and pyridoxine. Growth factors and salts are frequently derived from complex media components such as yeast extract, molasses, cornsteep liquor and the like. It is moreover possible to add suitable precursors to the culture medium. The exact composition of the media compounds heavily depends on the particular experiment and is decided upon individually for each specific case. Information on the optimization of media can be found in the textbook “Applied Microbiol. Physiology, A Practical Approach” (Editors P. M. Rhodes, P. F. Stanbury, IRL Press (1997) pp. 53-73, ISBN 0 19 963577 3). Growth media can also be obtained from commercial suppliers, for example Standard 1 (Merck) or BHI (brain heart infusion, DIFCO) and the like.

All media components are sterilized, either by heat (20 min at 1.5 bar and 121° C.) or by filter sterilization. The components may be sterilized either together or, if required, separately. All media components may be present at the start of the cultivation or added continuously or batchwise, as desired.

The culture temperature is normally between 15° C. and 45° C., preferably at from 25° C. to 40° C., and may be kept constant or may be altered during the experiment. The pH of the medium should be in the range from 5 to 8.5, preferably around 7.0. The pH for cultivation can be controlled during cultivation by adding basic compounds such as sodium hydroxide, potassium hydroxide, ammonia and aqueous ammonia or acidic compounds such as phosphoric acid or sulfuric acid. Foaming can be controlled by employing antifoams such as, for example, fatty acid polyglycol esters. To maintain the stability of plasmids it is possible to add to the medium suitable substances having a selective effect, for example antibiotics. Aerobic conditions are maintained by introducing oxygen or oxygen-containing gas mixtures such as, for example, ambient air into the culture. The temperature of the culture is normally 20° C. to 45° C. and preferably 25° C. to 40° C. The culture is continued until formation of the desired product is at a maximum. This aim is normally achieved within 10 to 160 hours.

The fermentation broth can then be processed further. The biomass may, according to requirement, be removed completely or partially from the fermentation broth by separation methods such as, for example, centrifugation, filtration, decanting or a combination of these methods or be left completely in said broth. It is advantageous to process the biomass after its separation.

However, the fermentation broth can also be thickened or concentrated without separating the cells, using known methods such as, for example, with the aid of a rotary evaporator, thin-film evaporator, falling-film evaporator, by reverse osmosis or by nanofiltration. Finally, this concentrated fermentation broth can be processed to obtain the fatty acids present therein.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps. “Consisting essentially” means having the essential integers but including integers which do not materially affect the function of the essential integers.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described by example only and with reference to the following figures:

FIG. 1: Principles of Protein Glycan Coupling Technology in E. coli. An E. coli cell is transformed with three plasmids to generate the cloned glycoconjugate protein (GP). The plasmids encode the oligosaccharyltransferase PgIB, the biosynthetic polysaccharide locus and the carrier protein. The polysaccharide is synthesised on an undecaprenol pyrophosphate lipid anchor () within the cytoplasm, this is transferred to the periplasmic compartment where PgIB recognises the lipid link reducing end sugar and transfers the polysaccharide en bloc onto an acceptor sequon (D/E-X-N-X-S/T) on the carrier protein to produce the glycoconjugate protein (GP). IM, inner membrane; OM, outer membrane;

FIG. 2: F. tularensis SchuS4 O-antigen is expressed in E. coli DH5α cells. E. coli cells carrying the F. tularensis vector pGAB1 (containing O-antigen coding region) and empty pGEM-T Easy vector respectively, stained with DAPI to visualise nucleic acid in blue (panels a and b) and probed with mAb FB11 and Alexa Fluor® 488 conjugated secondary antibody (panels c and d). Images are shown at 100× magnification;

FIG. 3: F. tularensis O-antigen is conjugated to ExoA by CjPgIB in E. coli CLM24 cells. Two colour immunoblots performed on HIS tag purified ExoA using mouse mAbFB11 (green) and rabbit anti 6×HIS tag antibody (red). Lane 1, E. coli CLM24 carrying pGAB2, pGVXN150, pGVXN115 (non-functional CjPgIB control); lane 2, pGAB2, pGVXN150, pGVXN114 (functional CjPgIB); lane 3, pGVXN150 only; Panel 2b, close up view of HIS-tagged purified ExoA attached to various chain lengths of F. tularensis O-antigen. M=marker IRDye® 680/800 protein marker. pGVXN150 contains ExoA, pGAB2 contains F. tularensis O-antigen, pGVXN114 and pGVXN115carry a functional and non-functional CjPgIB respectively;

FIG. 4: Vaccination with test glycoconjugate increases host survival compared to LPS and controls. Balb/C mice were vaccinated with three doses of 10 ug glycoconjugate+SAS, LPS+SAS or 10 μg LPS (n=10 per group). Mice were challenged 5 weeks following final vaccination with 100 CFU of F. tularensis strain HN63 via the i.p. route. Both LPS, LPS+SAS and test glycoconjugate provided improved protection when compared to the relevant unvaccinated controls (P<0.001) and the SAS alone provided no survival benefit (P>0.05) as analysed by stratified log rank test. The test glycoconjugate provided significantly better protection than the LPS alone or LPS+SAS vaccine (P<0.001 and P=0.025 respectively).

FIG. 5: Mice vaccinated with test glycoconjugate shows a reduced bacterial load in spleens compared to LPS and controls. Unvaccinated, SAS vaccinated, 10 μg LPS, or 10 μg test glycoconjugate+SAS vaccinated mice were challenged with 100 CFU of F. tularensis strain HN63 via the i.p. route. Spleens were removed 3 days post infection from each group (n=5) and assessed for bacterial CFUs. Logarithm data were analysed using a general linear model and Bonferroni's post tests. There was no difference in bacterial load between SAS vaccinated and unvaccinated mice (P>0.05) but the 10 μg LPS or 10 μg test glycoconjugate vaccinations had significantly decreased bacterial load when compared to relevant controls (P<0.001). Mice vaccinated with the test glycoconjugate+SAS had significantly reduced bacterial numbers in the spleen compared to LPS (P<0.05).

FIG. 6: Reduced inflammatory responses seen in LPS and glycoconjugate vaccinated mice compared to controls. Unvaccinated, SAS vaccinated, 10 μg LPS or 10 μg test glycoconjugate vaccinated mice were challenged with 100 CFU of F. tularensis strain HN63 via the i.p. route. Spleens were removed 3 days post infection from each group (n=5) and assessed for cytokine response. Levels of IL-6, MCP-1 and IFN-γ, were measures by CBA; all cytokine data pg/spleen. Individual points represent individual samples with line indicating the mean. Logarithm data was analysed using a general linear model and Bonferroni's post tests. Cytokine production (IL-6, MCP-1 and IFN-γ) was comparable between controls (untreated and SAS) and the two vaccine treated groups (LPS and glycoconjugate). Cytokine concentration was reduced in vaccinated mice compared to relevant controls (P<0.05) and the experiments 1 and 2 did not differ from each other (P>0.05);

FIG. 7: Increased IgG response in glycoconjugate vaccinated mice animals 7 days prior to challenge. Increased LPS specific IgG was observed in the glycoconjugate+SAS vaccinated group when compared to animals vaccinated with LPS only (P<0.001);

FIG. 8: Pilot study of vaccine candidates and relevant controls. Balb/C mice were vaccinated with three doses, 2 weeks apart with candidate vaccine or relevant controls (n=10 per group). Mice were challenged 5 weeks following final vaccination with 100 CFU of F. tularensis strain HN63 via the i.p. route. 0.5 of product per time point were assessed. Mice vaccinated with 0.5 μg test glycoconjugate with SAS (P<0.05) and the 0.5 μg LPS vaccines (P<0.001) survived longer than controls as determined by log rank test. Glycoconjugate, F. tularensis O-antigen ExoA glycoconjugate; sham glycoconjugate, C. jejuni 81116 heptasaccharide ExoA glycoconjugate; and

FIG. 9: F. tularensis LPS specific IgM levels observed in vaccinated mice 1 day prior to challenge. There were no differences between LPS specific IgM levels in the glycoconjugate and SAS vaccinated group when compared to animals vaccinated with LPS only group (P>0.05). We observed no evidence of the LPS-specific IgM titres differing between experiments (P>0.05).

FIG. 10 (SEQ ID 1) Amino acid sequence of carrier protein ExoA (Pseudomonas aeruginosa)

FIG. 11 (SEQ ID NO: 2) Amino acid sequence of carrier protein TUL4 (Francisella tularensis)

FIG. 12 (SEQ ID NO: 3) Amino acid sequence of carrier protein FTT1713c (Francisella tularensis)

FIG. 13 (SEQ ID NO: 4) Amino acid sequence of carrier protein FTT1695 (Francisella tularensis)

FIG. 14 (SEQ ID NO: 5) Amino acid sequence of carrier protein FTT1269c (Francisella tularensis)

FIG. 15 (SEQ ID NO: 6) Amino acid sequence of carrier protein FTT1696 (Francisella tularensis)

FIGS. 16A-16F (SEQ ID NO: 7) Nucleotide sequence encoding the Francisella O-antigen biosynthetic polysaccharide

FIG. 17: SEQ ID NO: 8 nucleotide sequence encoding the oligosaccharyltransferase PgIB (C. jejuni)

FIG. 18: SEQ ID NO: 9 Pgl B amino acid sequence (C. jejuni)

FIG. 19: SEQ ID NO: 16 nucleotide sequence encoding the oligosaccharyltransferase PgIB (Campylobacter sputorum)

FIG. 20 SEQ ID NO: 17 Amino acid sequence (full length) of PgIB (Campylobacter sputorum)

FIG. 21 HIS tag purified DNAK protein from cultures of Escherichia coli CLM24. Comparison of 2 plasmid system (chromosomally encoded PgIB) and standard 3 plasmid system. Lanes 1/3/5, three biological replicates of DNAK purified from the two plasmid system; Lanes 2/4/6, three biological replicates of DNAK purified from the 3 plasmid system. Three plasmid system consists of pGAB2 coding for Francisella tularensis O antigen, pEC415DNAK coding for F. tularensis DNAK and pGVXN114 coding for PgIB.

FIG. 22: The F. tularensis O-antigen is conjugated to ExoA. Treatment of the glycoconjugate with proteinase K to degrade ExoA results in loss of the O-antigen ladder at the corresponding size. Western blot was performed with monoclonal antibody FB11. A, Markers; B, proteinase K digested ExoA F. tularensis O-antigen glycoconjugate; C, glycoconjugate heated to 50° C. o/n without proteinase K. S1.2; Silver stained ExoA F. tularensis O-antigen glycoconjugate.

FIG. 23: Comparison of LPS-specific IgM levels from the glycoconjugate and LPS vaccine groups. Panel a, combined anti glycan and anti HIS signal; panel b, anti HIS signal only; panel c, anti-glycan signal only. Lane 1, ₂₆₀DNNNS₂₆₄ altered to ₂₆₀DNQNS₂₆₄; Lane 2, ₄₀₂DQNRT₄₀₆ altered to ₄₀₂DQQRT₄₀₆; Lane 3, ₂₆₀DNNNS₂₆₄ altered to ₂₆₀DNQNS₂₆₄ and ₄₀₂DQNRT₄₀₆ altered to ₄₀₂DQQRT₄₀₆; Lane 4, exotoxin A encoded from pGVXN150.

DETAILED DESCRIPTION

TABLE 1 Strains and plasmids used Strain/plasmid Description Source E. coli DH5α F-φ80lacZΔM15 Invitrogen Δ(lacZYA-argF) U169 deoRrecA1 endA1 hsdR17 (rk−, mk+), gal- phoAsupE44λ - thi-1 gyrA96 relA1 E. coli XL-1 endA1 gyrA96(nalr)thi-1 Stratagene relA1 lac gln V44 F′[::Tn10 proAB+ laclq Δ (lacZ)M15] hsdR17(r_(k) ⁻m_(k) ⁺) E. coli CLM24 rph-l IN(rrnD-rrnE) 1, 5 ΔwaaL F. tularensis subs. Type A strain DSTL, Porton tularensis strain SchuS4 Down laboratories F. tularensis subs. Type B strain, isolated in Green, M., et al., holarctica strain HN63 Norway from an infected Efficacy of the live attenuated Hare Francisella tularensis vaccine (LVS) in a murine model of disease. Vaccine, 2005. 23(20): p. 2680-6 pGEM-T Easy TA cloning vector, amp^(r) Promega pLAFR1 Low copy expression Vanbleu E, Marchal K, vector, tet^(r) Vanderleyden J. Genetic and physical map of the pLAFR1 vector. DNA Seq. 2004 June; 15(3): 225-7. pGAB1 F. tularensis O antigen This study coding region inserted into MCS of pGEM-T easy pGAB2 F. tularensis subs. This study tularensis strain SchuS4 O antigen coding region inserted into Ecorl site of pLAFR. pGVXN114 Expression plasmid for GlycoVaxyn CjPglB regulated from the Lac promoter in pEXT21. IPTG inducible, HA tag, Spec^(r). pGVXN115 Expression plasmid for GlycoVaxyn C. jejuninon functionalPglB due to a mutation at ₄₅₇WWDYGY₄₆₂ to ₄₅₇WAAYGY₄₆₂, regulated from the Lac promoter in pEXT21. IPTG inducible, HA tag, Spec^(r). pGVXN150₂₆₀DNQNS₂₆₄ Expression plasmid for This study Pseudomonas aeruginosa PA103(DSM111/) Exotoxin A with the signal peptide of the E. coliDsbA protein, two inserted bacterial N-glycosylation sites, AA at position 262 altered from N to Q and a hexahis tag at the C-terminus. Induction under control of an arabinose inducible promoter, Amp^(r) pGVXN150₄₀₂DQQRT₄₀₆ Expression plasmid for This study Pseudomonas aeruginosa PA103(DSM111/) Exotoxin A with the signal peptide of the E. coliDsbA protein, two inserted bacterial N-glycosylation sites, AA at position 404 altered from N to Q and a hexahis tag at the C-terminus. Induction under control of an arabinose inducible promoter, Amp^(r) pGVXN150₂₆₀DNQNS₂₆₄/ Expression plasmid for This study ₄₀₂DQQRT₄₀₆ Pseudomonas aeruginosa PA103(DSM111/) Exotoxin A with the signal peptide of the E. coliDsbA protein, two inserted bacterial N-glycosylation sites, AA at position 262 and 404 altered from N to Q and a hexahis tag at the C-terminus. Induction under control of an arabinose inducible promoter, Amp^(r) pACYCpgl pACYC184 carrying the 5 CjPglB locus, Cm^(r) E. coli CedAPglB E. coli strain CLM24 with a This study chromosomally inserted IPTG inducible copy of PglB

Materials and Methods

Bacterial Strains and Plasmids

Escherichia coli strains were grown in LB at 37° C., 180 r.p.m. Antibiotics were used at the following concentrations; tetracycline 20 μg/ml, ampicillin 100 μg/ml, spectinomycin 80 μg/ml, chloramphenicol 30 μg/ml. The host strain for initial cloning experiments was E. coli XL-1, subsequent strains used for glycoconjugate production were E. coli DH5α and CLM24 (Table 1). For efficacy studies, mice were challenged with F. tularensis subsp. holarctica strain HN63. The bacterium was cultured on blood cysteine glucose agar plates (supplemented with 10 ml of 10% (wt/vol) histidine per litre) at 37° C. for 18 hours.

Cloning, Sequencing and Expression of the F. tularensis O Antigen Coding Region

DNA was prepared from the F. tularensis subsp. tularensis strain SchuS4 by phenol extraction as described by Karlsson et al. (2000). The O-antigen coding region was amplified using the primers FTfragment2rev (5′-GGATCATTAATAGCTAAATGTAGTGCTG-3′; SEQ ID 10) and Oant1ftfwd (5′-TTTTGAATTCTACAGGCTGTCAATGGAGAATG-3′; SEQ ID 11) using the following cycling conditions: 94° C., 15 sec, 55° C., 15 sec, 68° C., 20 min; 35 cycles using Accuprime TaqHifi (Invitrogen U.K.). This was cloned into the TA cloning vector pGEM-T Easy to generate the vector pGAB1. The plasmid pGAB1 was digested with EcoRI and the insert was subcloned into the vector pLAFR to generate the construct pGAB2.

Immunofluorescence Imaging of E. coli Cells Carrying F. tularensis O Antigen Coding Region

Immunofluorescence was carried out as previously described [17] with the modification that the IgG2a mouse monoclonal antibody FB11 was used to detect F. tularensis O antigen (1 μl/ml in 5% (v/v) FCS/PBS).

Production and Purification of Glycoconjugate Vaccine

E. coli CLM24 carrying the vectors pGAB2, pGVXN114 and pGVXN150 was grown for 16 h in 200 mL LB broth at 37° C., 180 r.p.m. This was used to inoculate 1.8 L of LB broth and further incubated at 110 r.p.m. 37° C. to an OD.600 nm reading of 0.4 to 0.6. L-arabinose was then added to a final concentration of 0.2% and IPTG to a final concentration of 1 mM to induce expression of exoA and CjpglB respectively; following 5 hours of incubation, 0.2% L-arabinose was added again and the culture left to incubate o/n.

Cells were harvested by centrifugation at 6,000 r.p.m. for 30 m, and pelleted cells were incubated at room temperature for 30 m in a lysis solution composed of 10× BugBuster protein extraction reagent (Novagen) diluted to 1× in 50 mM NaH2PO₄, 300 mM NaCl, 10 mM imidazole, pH 8.0 supplemented with 0.1% Tween, 1 mg/ml lysozyme and 1 μl/ml Benzonase nuclease (Novagen). Cell debris was removed by centrifugation at 10,000 r.p.m. for 30 m, the supernatant was collected and 1 ml Ni-NTA agarose (QIAgen) was added to the supernatant. The slurry-lysate was incubated for 1 h at 4° C. with shaking then loaded into 10 ml polypropylene columns (Thermo scientific). His tagged ExoA was purified according to manufacturer's instructions (QIA expressionist, QIAGEN) with the addition of 20% glycerol and 5% glucose to the elution buffer. Protein yields were estimated using a bicinchonic acid assay kit according to manufacturer's instructions (Pierce® Biotechnology BCA protein Assay Kit, U.S.A.).

For large-scale protein purification, material was isolated using GE Healthcare His Trap columns and an AKTA purifier with an imidazole gradient of 30-500 mM. The collected fraction containing ExoA glycosylated with F. tularensis O-antigen was further purified using a resource Q anionic exchange column (GE Healthcare) with a NaCl gradient from 0 to 500 mM in 20 mM TrisHCl pH 8.0. This generated a typical yield of 2-3 mg/ml of glycoconjugate per 2 L of E. coli culture.

The same techniques were used for the generation of the ‘sham’ C. jejuni heptasaccharide ExoA glycoconjugate encoded by pACYCpgl [18].

Using the E. coli chromosomally inserted strain CLM 24 CedAPglB: Escherichia coli strain CLM24 with a chromosomally inserted copy of pgIB were grown in Luria-Bertani (LB) broth at 37° C., with shaking. Antibiotics were used at the following concentrations: tetracycline 20 μg ml⁻¹ and ampicillin 100 μg ml⁻¹. Tetracycline was used to maintain the plasmid pGAB2 coding for Francisella tularensis O antigen and ampicillin was used to maintain the plasmid coding for the acceptor carrier protein.

Escherichia coli cells were grown for 16 h in 200 ml LB broth at 37° C., with shaking. This was used to inoculate 1.8 l of LB broth and further incubated with shaking at 37° C. until an OD600 reading of 0.4-0.6 was reached. At this point L-arabinose was added to a final concentration of 0.2 per cent and IPTG to a final concentration of 1 mM to induce expression of the acceptor protein and pgIB, respectively; after another 5 h of incubation, 0.2% L-arabinose was added again and the culture left to incubate overnight.

Cells were harvested by centrifugation at 5300 g for 30 min, and pelleted cells were incubated at room temperature for 30 min in a lysis solution composed of 10× BugBuster protein extraction reagent (Novagen) diluted to 1× in 50 mM NaH₂PO₄, 300 mM NaCl, 10 mM imidazole, pH 8.0 supplemented with 0.1 per cent Tween, 1 mg ml⁻¹ lysozyme and 1 μl ml⁻¹ Benzonase nuclease (Novagen). Cell debris was removed by centrifugation at 7840 g for 30 min, the supernatant was collected and 1 ml Ni-NTA agarose (QIAGEN) was added to the supernatant. The slurry-lysate was incubated for 1 h at 4° C. with shaking then loaded into 10 ml polypropylene columns (Thermo Scientific). His-tagged ExoA was purified by the addition of an elution buffer according to manufacturer's instructions (QIA expressionist, QIAGEN) containing 250 mM imidazole with the addition of 20 per cent glycerol and 5 per cent glucose.

Alternatively cells were grown in LB agar plates containing tetracycline, ampicillin, IPTG to a final concentration of 50 μM and L-arabinose to a final concentration of 0.2% for 16 h at 37 ° C. Cells were subsequently harvested by scraping and protein purified as indicated above.

Immunoblot Analysis

To verify transfer and presence of the F. tularensis O antigen, samples were analysed by western blotting. E. coli cells were grown o/n in 10 ml LB broth and diluted to an O.D.600 nm of 1.0. Cells were centrifuged at 13,000 r.p.m. for 10 min, supernatant was removed and cells were resuspended in 100 μl Laemmli buffer and lysed by boiling for 10 min before analysis by western blotting or silver staining. Mouse anti F. tularensis O-antigen monoclonal antibody FB011 (AbCam U.K.) was used at a dilution of 1:1,000, rabbit anti HIS monoclonal antibody was used to detect ExoA at a dilution of 1:10,000 (AbCam U.K.). Secondary antibodies used were goat anti mouse IRDye680 and IRDye800 conjugates used at 1:5000 dilutions. Signal detection was undertaken using the Odyssey® LI-COR detection system (LI_COR Biosciences GmbH).

Cytokine Response Analysis

Spleen supernatants were assessed using mouse inflammatory cytometric bead array kit (CBA-BD biosciences) for IL-10, IL-12p70, IFN-γ, IL-6, TNF-α, and MCP-1. Samples were incubated with the combined capture bead cocktail, and incubated for 1 h at room temperature. Following incubation, PE detection antibodies were added and incubated for a further 1 h. Samples were then washed and resuspended in FACS buffer. Cytokine concentrations were measured via quantification of PE fluorescence of samples in reference to a standard curve.

BALB/c Mouse Challenge Studies

Female Balb/C mice were obtained from Charles River Laboratories (Kent, U.K.) at 6-8 weeks of age. The pilot study was done in groups of 10 mice immunised with either 0.5 μg F. tularensis LPS, 0.5 μg F. tularensis glycoconjugate, 0.5 μg F. tularensis glycoconjugate+SAS, 0.5 μg ‘sham’ glycoconjugate+SAS, 0.5 μg ‘sham’ glycoconjugate or SAS only. One group of mice were left untreated as challenge efficacy controls. Immunisations occurred on days 0, 14 and 28 via intra-peritoneal (IP) route. Mice were challenged 35 days post-immunisation with 100 CFU of F. tularensis strain HN63 by the IP route, delivered in 0.1 ml. Subsequent experiments used the same schedule with 15 mice per group and doses of 10 μg of material per immunisation. Four weeks following final vaccination 5 mice from each group were tail bled to obtain sera for antibody analysis and culled at day 3 post-infection with spleens harvested to analyse bacterial load and cytokine response. For the enumeration of bacteria, spleen samples were homogenized in 2 ml of PBS through 40 μm cell sieves (BD Biosciences) and 100 μl aliquots were plated onto BCGA plates. F. tularensis LPS-specific IgM and total IgG levels were determined by ELISA as previously described [19]. All work was performed under the regulations of the Home Office Scientific Procedures Act (1986).

Statistical Analysis

Statistical analyses were performed using the program PASW (SPSS release 18.0). Survival data was analysed by pair-wise Log Rank test stratified by experiment. Cytokine and bacterial load data were analysed using univariate general linear models, using Bonferroni's post tests to further clarify significant differences.

Production and Purification of Glycoconjugate Vaccine

E. coli CLM24 carrying the vectors pGAB2, pGVXN114 and pGVXN150 was grown for 16 h in 200 mL LB broth at 37° C., 180 r.p.m. This was used to inoculate 1.8 L of LB broth and further incubated at 110 r.p.m. 37° C. until an O.D600 reading of 0.4 to 0.6 was reached. At this point L-arabinose was added to a final concentration of 0.2% and IPTG to a final concentration of 1 mM to induce expression of exoA and Cjpg/B respectively; after another 5 hours of incubation, 0.2% L-arabinose was added again and the culture left to incubate o/n.

Cells were harvested by centrifugation at 6,000 r.p.m. for 30 m, and pelleted cells were incubated at room temperature for 30 m in a lysis solution composed of 10× BugBuster protein extraction reagent (Novagen) diluted to 1× in 50 mM NaH2PO4, 300 mM NaCl, 10 mM imidazole, pH 8.0 supplemented with 0.1% Tween, 1 mg/ml lysozyme and 1 μl/ml Benzonase nuclease (Novagen). Cell debris was removed by centrifugation at 10,000 r.p.m. for 30 m, the supernatant was collected and 1 ml Ni-NTA agarose (QIAgen) was added to the supernatant. The slurry-lysate was incubated for 1 h at 4° C. with shaking then loaded into 10 ml polypropylene columns (Thermo scientific). His tagged ExoA was purified by the addition of an elution buffer according to manufacturer's instructions (QIA expressionist, QIAGEN) containing 250 mM imidazole with the addition of 20% glycerol and 5% glucose. Protein yields were estimated using a bicinchonic acid assay kit according to manufacturer's instructions (Pierce® Biotechnology BCA protein Assay Kit, U.S.A.).

For large-scale protein purification, material was isolated using GE Healthcare HIS trap columns and an AKTA purifier with an imidazole gradient of 30 mM to 500 mM. The collected fraction containing ExoA glycosylated with F. tularensis O-antigen was further purified using a resource Q anionic exchange column (GE Healthcare) with a NaCl gradient from 0 to 500 mM in 20 mM TrisHCl pH 8.0. This generated a typical yield of 2-3 mg/ml of glycoconjugate per 2 L of E. coli culture.

The same techniques were used for the generation of the ‘sham’ C. jejuni heptasaccharide ExoA glycoconjugate. The plasmid coding for this heptasaccharide was pACYCpgl carrying the entire Cjpgl cluster from C. jejuni 81116 [1].

Protein Expression

Escherichia coli strain CLM24 with a chromosomally inserted copy of pglB were grown in Luria-Bertani (LB) broth at 37° C., with shaking. Antibiotics were used at the following concentrations: tetracycline 20 μg ml-1 and ampicillin 100 μg ml-1. Tetracycline was used to maintain the plasmid pGAB2 coding for Francisella tularensis O antigen and ampicillin was used to maintain the plasmid coding for the acceptor carrier protein.

Escherichia coli cells were grown for 16 h in 200 ml LB broth at 37° C., with shaking. This was used to inoculate 1.8 l of LB broth and further incubated with shaking at 37° C. until an OD600 reading of 0.4-0.6 was reached. At this point L-arabinose was added to a final concentration of 0.2 per cent and IPTG to a final concentration of 1 mM to induce expression of the acceptor protein and pglB, respectively; after another 5 h of incubation, 0.2 per cent L-arabinose was added again and the culture left to incubate overnight.

Cells were harvested by centrifugation at 5300 g for 30 min, and pelleted cells were incubated at room temperature for 30 min in a lysis solution composed of 10× BugBuster protein extraction reagent (Novagen) diluted to 1× in 50 mM NaH2PO4, 300 mM NaCl, 10 mM imidazole, pH 8.0 supplemented with 0.1 per cent Tween, 1 mg ml-1 lysozyme and 1 μl ml-1 Benzonase nuclease (Novagen). Cell debris was removed by centrifugation at 7840 g for 30 min, the supernatant was collected and 1 ml Ni-NTA agarose (QIAGEN) was added to the supernatant. The slurry-lysate was incubated for 1 h at 4° C. with shaking then loaded into 10 ml polypropylene columns (Thermo Scientific). His-tagged ExoA was purified by the addition of an elution buffer according to manufacturer's instructions (QIA expressionist, QIAGEN) containing 250 mM imidazole with the addition of 20 per cent glycerol and 5 per cent glucose.

EXAMPLES Example 1 Expression of the F. tularensis SchuS4 O-antigen in E. coli DH5α Cells

The 20 kb F. tularensis SchuS4 O-antigen coding region was PCR amplified and cloned into pGEM-T Easy to generate the plasmid pGAB1. All bacterial strains and vectors used in this study are summarized in table 1. To confirm O-antigen expression and transport to the outer cell surface of E. coli, pGAB1 was transformed into DH5α cells and probed by immunofluorescence using mAb FB11, specific to the F. tularensis O-antigen. FIG. 2C demonstrates the expression of the O-antigen on the surface of E. coli DH5α cells, which is absent in the vector alone control (FIG. 2D).

Example 2 CjPgIB can Transfer F. tularensis O-antigen to the Acceptor Protein Exotoxin A

In order to generate a strong T-cell response and lasting immunity, a highly immunogenic protein is required as a carrier for the F. tularensis O-antigen. The selected carrier protein was an inactivated form of the P. aeruginosa Exotoxin A variant L552V, AE553 (ExoA) was selected [20]. The plasmid pGAB2 containing the F. tularensis O-antigen expressed in the low copy vector pLAFR1 [21] was transformed into E. coli CLM24 cells along with the plasmids pGVXN114 and pGVXN150 which contain CjPgIB and ExoA respectively. As negative glycosylation controls, CLM24 cells were transformed with either pGVXN150 alone or with the combination of pGAB2, pGVXN150 and pGVXN115, the latter coding for an inactive version of CjPgIB [18]. Following overnight induction of CjpglB and exoA expression with 1 mM IPTG and 0.2% L-arabinose (w/v) respectively, cells were lysed and HIS tagged ExoA purified using Nickel columns. Elution fractions from each sample were separated by SDS PAGE and tested by immunoblotting with mAbFB011 specific for F. tularensis LPS. A band matching the expected size of ExoA and an O-antigen ladder pattern could only be seen when a functional CjPgIB was present (FIG. 3, lanes 2 and 2b). In the absence of a functional CjPgIB there was no cross-reaction with mAbFB11 (FIG. 3, lanes 1 and 3). To demonstrate that the O-antigen was bound to the carrier protein, HIS tagged ExoA F. tularensis O-antigen conjugate was purified and digested with Proteinase K. The disappearance of the O-antigen ladder after Proteinase K treatment but not in the untreated control confirmed that the O-antigen was anchored to ExoA (data not shown).

Example 3 Vaccination with the Glycoconjugate Provides Significant Protection against F. tularensis subsp. holarctica Infection in Mice

In a pilot study we compared LPS alone against the glycoconjugate vaccine and monitored antibody levels and murine survival. The Sigma Adjuvant System® was selected for use in this study because it is based on monophosphoryl lipid A (MPL), a low toxicity derivative of LPS that has been demonstrated to be a safe and effective immunostimulant [22]. In order to demonstrate the specificity of the glycoconjugate we used controls including mice with SAS adjuvant alone, unvaccinated mice and mice vaccinated with a ‘sham’ glycoconjugate control (C. jejuni heptasaccharide conjugated to ExoA). Only mice vaccinated with 0.5 test glycoconjugate+SAS (P<0.05) or 0.5 μg LPS (P<0.001) demonstrated increased survival compared to the appropriate controls as determined by log rank test (FIG. 22). These candidates were selected for further assessment at higher doses and an additional group consisting of LPS+SAS was also added as a further control. Protection was compared between mice immunised with either 10 μg glycoconjugate+SAS, 10 μg LPS or 10 μg LPS+SAS. All three vaccines were protective when compared to the unvaccinated mice (P<0.001), while the SAS adjuvant alone did not elicit any protection (P>0.05) (FIG. 4). This experiment also indicated that LPS+SAS did not elicit the same level of protection as the glycoconjugate+SAS combination (P<0.05) and thereafter LPS+SAS was deemed unnecessary for testing. The study was repeated in order to provide further bacterial organ load and immunological response data and no statistically significant difference was found between replicates.

Example 4 Mice Vaccinated with Test Glycoconjugate and Challenged with F. tularensis subsp. holarctica have Lower Bacterial Loads and Pro-Inflammatory Cytokines 3 Days Post Challenge

Three days post challenge 5 mice per group were sacrificed and bacterial loads in the spleens and inflammatory responses were evaluated (FIG. 5). FIG. 5 shows the bacterial loads from vaccine with 10 μg of each candidate. Mice that were immunised with the glycoconjugate+SAS or LPS both had significantly decreased bacterial loads in spleens (P<0.01) when compared to the SAS and unvaccinated controls. Mice vaccinated with glycoconjugate+SAS had significantly less bacteria compared to those vaccinated with LPS alone (P<0.05). Inflammatory cytokine profiles between the different vaccine groups were also analysed (FIG. 6). Reduced levels of inflammatory cytokines were seen in mice vaccinated with glycoconjugate+SAS and LPS alone (P<0.05), corresponding with decreased bacterial loads. There was no significant difference between cytokine profiles for both experiments (P>0.05).

Example 5 Vaccination with the F. tularensis Glycoconjugate Induces a Greater IgG Immune Response

The levels of LPS-specific IgG were assessed in mice 7 days prior to challenge for both experiments. Increased LPS-specific IgG was observed in the glycoconjugate+SAS vaccinated group when compared to animals vaccinated with LPS only (P<0.001). Although experiment 2 had higher levels of antibody (P<0.01), we observed no difference in pattern between experiments (P>0.05) (FIG. 7). No significant differences were observed between LPS-specific IgM levels from the glycoconjugate and LPS vaccine groups (FIG. 23).

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1. A process for manufacturing a glycoconjugate polypeptide, comprising: i) providing a bacterial cell in cell culture medium, wherein said bacterial cell is genetically modified to include: a) a nucleic acid molecule comprising the nucleotide sequence of the Francisella O-antigen biosynthetic polysaccharide locus set forth in SEQ ID NO: 7; b) a nucleic acid molecule comprising the oligosaccharyltransferase nucleotide sequence set forth in SEQ ID NO: 8 or a functional variant thereof, wherein said functional variant comprises a nucleic acid molecule the complementary strand of which hybridizes under stringent hybridization conditions to the sequence set forth in SEQ ID NO: 8 and wherein said nucleic acid molecule encodes an oligosaccharyltransferase; and c) a nucleic acid molecule comprising a nucleotide sequence of a carrier polypeptide, wherein the carrier polypeptide comprises one or more T-cell dependent epitopes and one or more amino acid sequences having the amino acid motif D/E-X-N-X-S/T, wherein X is any amino acid except proline, wherein the bacterial cell is adapted for expression of each nucleic acid molecule set forth in a), b) and c); ii) growing the bacterial cell in the cell culture medium, wherein the oligosaccharyltransferase of b) glycosylates the carrier polypeptide of c) to form a glycoconjugate polypeptide comprising a Francisella O-antigen; and iii) isolating the glycoconjugate polypeptide comprising a Francisella O-antigen from the bacterial cell or the cell culture medium, thereby manufacturing a glycoconjugate polypeptide.
 2. The process according to claim 1, wherein at least the oligosaccharyltransferase is integrated into the bacterial genome of said bacterial cell.
 3. The process according to claim 1, wherein one or more nucleic acid molecules encoding the carrier polypeptide is integrated into the bacterial genome of said bacterial cell.
 4. The process according to claim 1, wherein said Francisella O-antigen comprises 4)-α-D-GalNAcAN-(1-4)-α-D-GalNAcAN-(1-3)-β-D-QuiNAc-(1-2)-β-D-Qui4NFm-(1-), wherein GalNAcAN is 2-acetamido-2-deoxy-O-D-galact-uronamide, 4NFm is 4,6-dideoxy-4-formamido-D-glucose and the reducing end group QuiNAc is 2-acetamido-2,6-dideoxy-O-D-glucose.
 5. The process according to claim 4, wherein said Francisella O-antigen is a tetrasaccharide.
 6. A glycoconjugate polypeptide obtained by the process according to claim
 1. 7. A vaccine composition comprising the glycoconjugate according to claim 6 and an adjuvant and/or carrier.
 8. An immunogenic composition comprising the glycoconjugate according to claim 6 and an adjuvant and/or carrier.
 9. A method for treating a Francisella infection, comprising administering an effective amount of the vaccine according to claim
 7. 10. A method for treating a Francisella infection, comprising administering an effective amount of the immunogenic composition according to claim
 8. 11. The method according to claim 9, wherein said Francisella infection is caused by Francisella tularensis.
 12. The method according to claim 10, wherein said Francisella infection is caused by Francisella tularensis. 